This invention relates to a laundry appliance having a door locking apparatus for maintaining the access door locked during the water extraction operation of the clothes-containing tub which is accomplished by spinning the tub at a relatively high speed that is thereby inherently dangerous if at this time the rotating tub is accessible.
In view of the above problem, prior art efforts have been directed to a number of interlock devices to accomplish the above-mentioned objectives. One such interlock device is shown in U.S. Pat. No. 3,272,935, wherein the patentees recognize that it is important to prevent the opening of the appliance lid during the spin cycle, and therefore provide an interlock latch mechanism which includes a switch which is operated by a striker member associated with the lid. Upon closure of the lid, the switch operates to energize a solenoid if the machine is in its spin cycle or to permit the solenoid to be energized when the spin cycle is reached. The solenoid attracts a pivoted arm which engages the striker member to securely lock the lid. Other examples of such a mechanism may be found in U.S. Pat. Nos. 3,638,457 and 3,602,015.
The use of a solenoid to operate the lid lock results in a costly and complex arrangement. More important, however, is the fact that the solenoid operates in an instantaneous manner when the circuit to the drive motor is interrupted. Therefore, it is possible to open the lid while the drum is spinning at a high speed while coasting to a stop. To overcome this problem, proposals have been made to provide a brake on the drive shaft of the machine which stops rotation upon the de-energization of the solenoid. Here again, however, the basic cost of the appliance is increased.
To overcome these problems, a proposal is set forth in U.S. Pat. No. 3,608,337, wherein the patentee proposes to hold an electrically operated door latch in a locked condition by the voltage developed by the motor during regenerative braking of the drum or cylinder at the end of the washing program. This is achieved by shunting the field and the armature of the motor, disconnecting the supply from a control thyristor, and running the motor as a generator using, initially, the residual magnetism of the field. While this arrangement accomplishes a desired result, it requires additional switching devices and does not eliminate the need for a solenoid.